Fingerprint sensing and matching is a reliable and widely used technique for personal identification or verification. In particular, a common approach to fingerprint identification involves scanning a sample fingerprint or an image thereof and storing the image and/or unique characteristics of the fingerprint image. The characteristics of a sample fingerprint may be compared to information for reference fingerprints already in a database to determine proper identification of a person, such as for verification purposes.
A particularly advantageous approach to fingerprint sensing is disclosed in U.S. Pat. No. 5,953,441 to Setlak and assigned to the assignee of the present invention. The fingerprint sensor is an integrated circuit sensor that drives the user's finger with an electric field signal and senses the electric field with an array of electric field sensing pixels on the integrated circuit substrate.
U.S. Pat. No. 6,289,114 to Mainguet discloses a fingerprint sensor that includes a finger sensing integrated circuit (IC). The finger sensing IC includes a layer of piezoelectric or pyroelectric material placed between upper and lower electrodes to provide electric signals representative of an image of the ridges and valleys of the fingerprint.
A particularly advantageous approach to multi-biometric fingerprint sensing is disclosed in U.S. Pat. No. 7,361,919 to Setlak, which is assigned to the assignee of the present invention and is incorporated in its entirety by reference. The Setlak patent discloses a multi-biometric finger sensor sensing different biometric characteristics of a user's finger that have different matching selectivities.
It may also be desirable to have a finger biometric sensor powered down or in a low power consumption mode until a finger is placed in a position to be sensed. The finger biometric sensor may desirably detect when the finger is in a sensing position and then activate itself and any other devices, such as processors, needed to perform the functions desired by the user.
Several approaches for detecting the presence of a finger in a desired position are known. Typically, in some approaches, a small part of a finger imaging system may be activated on a periodic basis to determine if a finger is present. A negative aspect of these approaches is that they dissipate power in the finger biometric sensor, and/or its supporting circuitry, during a time when the finger imaging system is waiting for the finger to appear. Quiescent power consumption while in a finger detect (waiting) mode drains a battery in a portable electronic device.
In an attempt to reduce the quiescent power consumption, some finger presence detection approaches have been proposed where the fingerprint sensor is mounted on a mechanically actuated electrical switching element. Finger pressure on the fingerprint sensor moves the switching element, causing the switch to close and activating sensor electronics or the supporting circuitry. While this approach may consume no quiescent current, it may be difficult to reliably implement because it requires the finger biometric sensor itself to be a moving part.
Several approaches to finger biometric sensors including a switch are disclosed in U.S. Pat. No. 4,120,585 to DePalma et al.; U.S. Pat. No. 6,522,773 to Houdeau; U.S. Pat. No. 6,912,299 to Hoshino et al.; and U.S. Pat. No. 7,266,226 to Hwang. U.S. Published Application No. 2004/0155752 to Radke also discloses a switch associated with a finger biometric sensor. U.S. Patent Application No. 2007/0076923 to Chiu, for example, discloses a finger sensing device that has a power control switch at the tip of the sensor panel, and a second switch underneath the finger sensor to initiate the finger sensing operation.
Other finger biometric sensors may include power controls integrated within the finger print imaging system, or adjacent the fingerprint sensor, such as disclosed in U.S. Published Application No. 2006/0239517 to Creasy et al. Still, other finger biometric sensors, such as disclosed in U.S. Pat. No. 5,940,526 to Setlak et al., include power control to only active portions of the finger sensor, thus resulting in a standby mode.
Still further, it may be desirable to provide the user with tactile feedback when a finger is placed on the biometric finger sensor. U.S. Published Application No. 2001/0017934 to Paloniemi et al. discloses a fingerprint sensor mounted on a switch. When the fingerprint sensor is tapped, the switch is operated and provides an audible and/or tactile feedback to a user, for example, by movement of a domed membrane. U.S. Published Application No. 2005/0111707 to Bohn et al. discloses a fingerprint scanner that provides a tactile and/or audible indication from an end of scan switch located on a housing frame.
U.S. Published Application No. 2006/0239517 to Creasey et al., as briefly described above, further discloses a finger sensor mounted on a housing of a device and providing feedback to a user in the form of physical feeling. A platen receives a user's finger and is coupled to a base of the housing. An activation sensor, which may be a piezoelectric sensor, is coupled to the platen and detects force on the platen in response to a user's finger pressed on the sensor.